1. Field of the Invention
The present invention relates to an optical pickup that writes and reads information to and from a disc in an optical disc drive or the like and an objective lens driving apparatus equipped with the optical pickup.
2. Description of the Invention
The configuration of the optical disc drive is described below. The optical disc drive is comprised of: a spindle motor for rotating an optical disc; an optical pickup for writing and reading information to and from each optical disc; a feeding mechanism for moving the optical pickup in the direction of the radius of each optical disc; each control circuit that controls the mechanism; and a controller that comprehensively controls regenerative signals from each optical disc and write signals to each optical disc. The optical pickup is a direct mechanism that writes and reads information to and from each optical disc in the above configuration.
Hereafter, description will be given to the operation of the optical disc drive including the optical pickup as a principal component. To read or write information from and to an optical disc, a laser is applied from the optical pickup onto the optical disc loaded into the optical disc drive. The spot of the laser is focused on the data surface of the optical disc and focusing control is carried out. Thereafter, the disc is rotated to carry out data track alignment and tracking control is similarly carried out. Thus optical information on the optical disc is converted into electrical information through the optical pickup and then it is transmitted as data to the controller of the optical disc drive. The optical disc drive receives signals from the optical pickup as mentioned above and transmits and receives data to and from a personal computer or the like.
The optical pickup writes and reads data to and from each optical disc as mentioned above. The objective lens driving apparatus is a mechanism for focusing a laser on each optical disc. The objective lens driving apparatus is comprised of: a holder that holds an objective lens; coils that cause the holder to produce magnetic driving force; a magnet that gives a magnetic field to cause the coils to produce magnetic propulsive force; and an elastic support member for holding the objective lens as a moving part. Three different types of coils are used as the above-mentioned coils: a focusing coil for driving the holder in the direction of the normal to the optical disc surface (this direction will be hereafter referred to as focusing direction); a tracking coil for driving the holder in the direction of the data tracks of each optical disc (this direction will be hereafter referred to as tracking direction); and a tilt coil for tilting the holder toward the direction of the radial direction of the optical disc.
In recent optical discs, their densities have been more and more increased and this is coped with mainly by shortening the wavelength of laser. Optical disc drives are used in personal computers and the like. A shift of personal computers to notebook computers has been accelerated and optical disc drives are also required to be reduced in size. Therefore, also with respect to optical pickups used in optical disc drives, it is indispensable to cope with density growth and yet reduce their thickness. Short-wavelength lasers incorporated in optical pickups provided for high densities are high in sensitivity to aberration due to the relative tilt between an optical disc and an objective lens; therefore, it is necessary to control the relative tilt between the objective lens and the optical disc. The relative tilt between an objective lens and an optical disc is influenced by the positional relation between the above coils and the magnet and an error in the position of supporting the moving part including the objective lens. The following documents describe conventional technologies related to a structure in the position of supporting a moving part including an objective lens:
Patent Document 1 discloses a structure in which an objective lens holding member is provided with a V-shaped groove and a wire is fixed in a gap between it and a retaining member as a different member formed into a V shape.
Patent Document 2 discloses a structure in which a member for holding one elastic support member is configured as a different structure and this member is attached to and fixed on an objective lens holder.    [Patent Document 1] Japanese Unexamined Patent Publication No. Hei 7(1995)-210883 (page 4, FIG. 2)    [Patent Document 2] Japanese Unexamined Patent Publication No. Hei 1(1989)-260641 (page 4, FIG. 2)
In the structure disclosed in Patent Document 1, the elastic support member is clamped by a different member and the elastic support member can be positioned in the focusing direction and the tracking direction. With this structure, however, the direction of the length of the elastic support member is not fixed and a positional error is produced in this direction. When the objective lens is driven, therefore, the support stiffness for the objective lens holder becomes out of balance due to a stiffness difference between elastic support members. As a result, the objective lens is tilted.
In the technology disclosed in Patent Document 2, positioning on the objective lens holder is carried out by a different member attached to the elastic support member. Therefore, the elastic support member can be reliably positioned. However, since only one elastic support member is positioned on the objective lens holder, the following takes place when multiple elastic support members are used: the distance between elastic support members depends on the accuracy of fabrication of the objective lens holder and a different member attached to the elastic support members. Therefore, high fabrication accuracy is required and this is not adequate to price reduction.
Therefore, it is necessary to devise the structure of an objective lens driving apparatus for optical pickups in which when an objective lens is driven, it is possible to suppress the relative tilt between an optical disc and the objective lens and yet stably achieve density enhancement.